2864 Inorganic Chemistry, Vol. 14, No. I I , I975 Contribution from the Research School of Chemistry, Australian National University, Canberra, A C T . 2600, Australia
Trapping of Labile Cobalt(II1) Complexes. Characterization of the Perchloratopentaamminecobalt(111) Ion
AIC5039 1K
Treatment of the complex ion (NH3)sCoO==SMe23+ with aqueous Cl2 results in the very rapid substitution of the dimethyl sulfoxide ligand by water and anions present in solution. The reacion stoichiometry is (NH,)SCoO=SMe,3t + C1, (1 -x)(NH,),COOH,~'
H,O, X-
+ 2H,O + X(NH~)~COX'+ + (CH,),SO, + 2HC1
Dimethyl sulfone was the sole organic product (established by 1H NMR spectroscopy on the reaction mixture and isolation with gravimetric quantitation and physical characterization: analysis, ir, 1H NMR, melting point, and mixture melting point comparisons with authentic material). The Co(II1)-containing products were characterized by ionexchange chromatographicseparation and visible spectroscopy. In the presence of acids HX (X- = C1-, N03-, HSOc) containing anions which form slowly aquating (NH3)sCoX2+ complexes the oxidation was observed as a simple first-order process (in the presence of excess Clz), with the observed rate constant showing a linear dependence on Cl2 concentration (Table I). In the presence of other acids (X- = CF3S03-, clod-) known or expected to form relatively labile (NH3)5CoX2+ complexes, consecutive first-order reactions were observed, one rate then being independent of Cl2 concentration and the other still showing a first-order dependence (Table I). In neither system were the rates dependent on acidity when allowance was made for the dependence of the Cl2 hydrolysis equilibrium on H+ concentration. In constant ionic strength mixtures of, for example, HC1 and HC104 a change from a single- to a double-rate process was detected as the HC104 concentration increased. An obvious rationalization of these data was inferred when it was recognized that the chlorine-independent rate in CF3S03H solutions corresponded to the independently measured rate constant for ( N H ~ ) ~ C O O ~ S aquation.2 C F ~ ~ + Thus it was concluded that oxidation in HC104 yielded some rapidly aquated (NH3)5CoOC1032+ ( k E 0.1 sec-1, 25", p = 1.0). To support this interpretation, efforts were made to detect the perchlorato complex in other systems where its transient presence might be anticipated. By choice of conditions (0.8 M HC104,O.l M Hg(C104)2) such that mercury(I1)-catalyzed removal of halide from (NH3)sCoBrz+and (NH3)jCoI2+ was complete in
